1. Field of the Invention
This invention relates to accumulators used in the suction line between the evaporator and the compressor in a refrigeration or air conditioning system and also relates to filter-driers which are used in such systems for filtering and dehydrating the refrigerant and oil in their liquid and vapor states.
2. Review of the Prior Art
In air conditioning, refrigerating, heat pump, and hot gas defrost systems of the prior art, filters and driers are essential components for removing harmful contaminants and protecting the motor compressor, the heart of any such system, which is called upon today to withstand increasingly severe operational conditions because market conditions are requiring smaller and more compact systems and higher speed compressors which subject the unit to higher temperatures and pressures and tend to shorten its life and increase the danger of premature breakdown.
Because the electrical portion of the motor is in direct contact with the refrigeration circuit, the chemical environment to which it is exposed is of prime importance. In addition, it is subject to damage from solids which must be prevented from reaching the compressor. These materials, in spite of utmost care in assembling and cleaning out a system, seem to be always present and are frequently not dislodged until the system is initially started up. They are major contributors to hermetic motor burn-outs and are also the cause of mechanical damage to close-tolerance parts by abrasive action.
At the present time, a system sanitizing approach is used to isolate the motor compressor from three general categories of contaminants which play important roles in compressor failure. These are: (1) harmful soluble chemicals; (2) damaging liquids and solids; and (3) oxygen present in air as a non-condensible.
Liquid line filter-driers are used to remove the broad spectrum of soluble contaminants, which include water, acids, oil breakdown products, tars, resins, gums, and dirt of relatively large particle size. The resins and gums are absorbed, and the dirt is filtered out. Such receiver driers are described in U.S. Pat. No. 3,118,288 and U.S. Pat. No. 3,785,164. They generally include a dessicant such as a molecular sieve or alumina and a flow directing means for forcing the liquid to pass through the dessicant.
However, vapor-phase filters having very little pressure drop are being increasingly used in recent years. Such vapor-phase filters are designed to remove harmful particles too small for filter-driers to take out in the liquid line, in addition to materials which are present in the system beyond the point where the liquid line filter-drier is installed.
Used in conjunction with a liquid line filter-drier, a vapor-phase filter effectively isolates the motor compressor from finely divided steel and other metallic particles which are believed to be the major cause of motor burn-outs when carried to the windings by high-velocity suction gas. These offending particles include metal chips, solder flux, copper oxide, iron rust, carbon, corrosion solids, and the like which contribute to motor burn-out or cause compressor damage through abrasion. However, a suction-side filter will filter out gross quantities of the foreign materials as small as 5 microns (0.0002 inch) in diameter, with negligible pressure drop while permitting high rates of gas flow in the suction line. Such vapor-phase filters are necessarily large in volume as compared to liquid line filter-driers.
Compressor damage is also caused by slugging of refrigerant and oil which typically occurs when a refrigeration or air conditioning system has been idle for an extended period. The suction effect of the compressor, when starting up after such idleness, creates such a low pressure that both liquid and vapor are pulled out of the evaporator and reach the compressor unless a means is provided for separating the liquid from the vapor and accumulating the liquid until it can be gradually re-introduced into the system as needed in the form of harmless droplets mixed with the vapor.
Excessive quantities of liquid refrigerant dilute the oil, wash out bearings, and in some cases cause complete loss of oil in the crankcase of the compressor because of the high solubility of the oil in the refrigerant. Because compressors are designed to compress vapors, not liquids, such accumulations or "slugs" also can result in broken valve reeds, pistons, rods, crank shafts, and the like parts of a compressor.
Thus a storage component in the form of an uprightly disposed cylinder is commonly added to the suction side of the refrigeration or air conditioning system to act as a reservoir for temporarily holding the excess oil-refrigerant mixture and returning it at a rate that the compressor can safely handle. Such an accumulator usually can hold from about one-half to about two-thirds of the oil-refrigerant mixture that is within the system.
In such accumulators, the total vapor and liquid-oil refrigerant mixture must flow through the accumulator which generally comprises a deep plenum chamber and a J-shaped pickup tube. This tube has an inlet which is disposed high above the bottom of the chamber to receive vapor but not liquid entering the chamber through the inlet port, and one or more orifices near the bottom bend of the pickup tube for gradually picking up liquid, including portions of the oil layer, by entrainment in the vapor flow passing through the bottom bend, enroute to the compressor.
Various suction accumulators have been designed with baffling and flow directing devices for gradual pickup of liquid by a flowing stream of vapor and for storing sudden surges of liquid refrigerant within the plenum chamber. U.S. Pat. Nos. 3,488,678; 3,698,207; 3,754,409; 3,796,064; and 3,938,353 are examples of such prior art devices. Their designs have sought to minimize inherent low efficiency with respect to pressure drop through the devices because pressure drop in the suction line of a refrigeration or air conditioning system adversely affects the total system capacity and the cost of operation. Another design objective has been to return in a gradual way a portion of the accumulated liquid refrigerant and the vapor as entrained mist or droplets of such minimal size as to be incapable of damaging the compressor.
In view of the limited space that is available adjacent to modern engines and refrigeration and air conditioning systems, both stationary and mobile, and the need for both filtering and liquid accumulation, it is highly desirable to be able to combine the functions and the space requirements of an accumulator and a filter and additionally highly desirable to be able to include the protective function of vapor-state drying within the same device.